| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2005: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Research Abstract |
Experimental studies have been conducted on the turbulent mixing in T-junctions with square cross sections and, based on the results of measurements, an effective method of its promotion and control has been developed. We have tested two types of mixing T-junctions. One is the counter-flow type T-junction in which the main and branch flows collide head-on in the T-junction and the mixed fluid flows down the mixing channel that is connected to the main and branch channels at right angles. The other is the cross-flow type T-junction, in which the branch is connected to the main channel at right angles.
In the counter-flow type T-junction, detailed characteristics of the velocity and concentration fields after the mixing have been investigated using simultaneous measurements by PIV and PLIF with high spatial/time resolutions : Rhodamine 6G has been dissolved in the main-channel fluid as fluorescence tracer. The three-dimensional characteristics of the velocity field and its influence on th
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e concentration field in the mixed flow were clarified. It has been found that the secondary flows are formed in the mixing channel and the high-concentration fluid is transported in the transverse direction. By POD analysis, the wobbling motion of the mixing layer in the spanwise direction, and a rational motion of the main-channel flow have been extracted from instantaneous fields. Moreover, the mechanism of turbulent mixing of two fluids has been analyzed based on the turbulent mass fluxes.
In the cross-flow type T-junction, the cold flow in the main channel and the hot flow in the branch merge in the T-junction. The flow structure and the mean temperature distributions have been measured by PIV and the thermocouple rake, respectively. Moreover, the turbulent heat fluxes in the thermal mixing layer have been measured by combining LDV and a cold-wire thermometer. A large separation bubble is observed in the main channel after the T-junction and strong turbulence is generated in the shear layer around it. This strong turbulence, however, appears below the thermal mixing layer, thus it does not contribute effectively to the turbulent thermal mixing of hot and cold flows. Based on these experimental results, we have proposed the mixing promotion and controlling method with small jets that are blown into the main channel at the upstream edge of the T-junction in the direction of 45 degrees against the main flow. Turbulence intensity in the upper part of the thermal mixing layer can be increased with these jets, and consequently the turbulent mixing of hot and cold airflows is promoted effectively. Moreover, the degree of thermal mixing can be controlled by changing the jet velocity. Less
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